More Room To Do What You Want
Living with someone else might not mean you need another bedroom, but another room for different furniture, entertainment, or workspace can do wonders. Sharing a bedroom and closet with your significant other might be more than enough, so get a separate living space for each other in the general house.
With a den in your apartment, one can watch the game while the other has friends over for drinks, or during the day one of you can retreat to a dedicated workspace to take important calls.